The present invention is directed to an automatic gain control circuit and more specifically, to a wide band automatic gain control amplifier for use with recurring signals. In accordance with the invention, each of the recurring signals is divided into a large number of time intervals and the gain of a plural stage amplifier is adjusted for each time interval independently of each of the other time intervals on the basis of the amplitude of previously received signals in the corresponding time interval.
Digitally controlled automatic gain control circuits are well known in the art. These circuits generally comprise a plurality of cascaded amplification stages interposed with attenuation circuits selectively switched into and out of the amplifier circuit. The values of the attenuation circuits are generally weighted in binary fashion to facilitate the control of the gain of the amplifier of a binary gain control word.
These amplifiers find particular utility as seismic amplifiers in which the amplitude of the input signal can be anticipated to grow successively weaker or successively stronger thereby facilitating the use of a clock controlled binary counter to successively increase or decrease the gain of the amplifier. Examples of this type of circuit are the McCarter U.S. Pat. No. 3,308,392 issued March 7, 1967, and the Godinez U.S. Pat. No. 3,376,557 issued Apr. 2, 1968.
Other patents such as the Sherer et al U.S. Pat. No. 3,525,948 issued Aug. 25, 1970, and the Lockheed, Jr. et al U.S. Pat. No. 3,464,022 issued Aug. 26, 1969, disclose the use of such amplifiers as automatic gain control circuits wherein the output signal is compared with predetermined limits and a gain control counter is pulsed up or down responsively thereto to adjust the gain of the amplifier in accordance with the amplitude of the output signal.
Still other patents such as the Neitzel U.S. Pat. No. 3,392,370 issued July 9, 1968, and the Nickels U.S. Pat. No. 3,510,682 issued May 5, 1970, have suggested the use of a digital computer or other circuit to generate a predetermined gain profile of digital signals to control the insertion of the attenuated elements into the various stages of the amplifier.
There are, however, certain situations when the circuits of the above identified patents do not provide the degree of amplification control desired. In the seismic art, for example, there may be large variations in the amplitude of the signals received by the amplifier due, not to the distance from the source, but to discontinuities, etc. In such circumstances, the gain adjustment suitable for one portion of the received signal may be entirely satisfactory for an immediately adjacent portion of the signal received. Where, for example, compressive waves initiated by detonation are successively generated, the method and circuit of the present invention permits adjustment of each of a plurality of small time intervals during which the signal is received to be amplified as a function of the amplitude of the signal from an earlier detonation in only the corresponding time interval rather than on the strength of the entire signal or on the strength of an earlier portion of the same signal.
A second problem associated with the known circuits is that of the transients continually generated as the gain of the various stages of the amplifier are adjusted as the signal is passed through the amplifier. These transient problems are solved in the present invention through the amplifier. These transient problems are solved in the present invention through the superimposition of the transients from each of the cascaded amplifier stages on the same minute portion of the received signal as it passes through the amplifier. By ignoring this small portion of the received signal during each of the time intervals, the amplified signal may be evaluated without distortion due to transients.
The present invention also has particular utility in radar systems in which a return signal from each radar transmitter pulse may be divided into a plurality of time intervals and the gain of the amplifier independently adjusted for each of the time intervals. Sensitivity may thereby be greatly enhanced.
It is accordingly an object of the present invention to provide a novel method and automatic gain control circuit wherein the gain of the circuit is independently adjusted during each of the large number of discrete time intervals independently of the gain of the amplifier during any of the other time intervals in which the signal is received.
Another object of the present invention is to provide a novel method and automatic gain control circuit which has particular utility with recurring signals whereby the gain of the amplifier for different portions of the received signal may be adjusted on the basis of the amplitude in previously received signals during the corresponding time interval.
Another object of the present invention is to provide a novel method and wide band automatic gain control amplifier in which the transients introduced through the switching of attenuation elements into and out of the circuit are superimposed.
A further object of the present invention is to provide a novel method and automatic gain control circuit in which the digital gain control signals are recirculated through a memory circuit to automatically interpose and intersignal delay.
These and other objects and advantages of the present invention will be apparent to one skilled in the art to which the invention pertains from the claims and from a perusual of the following detailed description when read in conjunction with the appended drawings.